When I dial out using iDrive, the call connects, but the Radio doesn't mute. Both the radio and the outgoing call are playing together; altho' I can barely hear the phone audio. What do I have to set to get the radio/CD/USB etc currently playing to MUTE when I dial out a phone call??? Anyone ever heard of this happening?

When I dial out using iDrive, the call connects, but the Radio doesn't mute. Both the radio and the outgoing call are playing together; altho' I can barely hear the phone audio. What do I have to set to get the radio/CD/USB etc currently playing to MUTE when I dial out a phone call??? Anyone ever heard of this happening?